Cartridge vane pump having enhanced cold start performance

ABSTRACT

A cartridge vane pump for a motor vehicle power steering system exhibits improved cold start performance. The pump includes a plurality of radially disposed vanes which are received within a rotor which is rotatably supported within a cylindrical cam ring defining two diametrically opposed pumping lobes. An inlet (upper) section and an outlet (lower) section engage the ends of the cam ring and define suitable passageways which provide fluid into and out of the pumping lobes. Under vane porting in the inlet section provides high pressure fluid to the inner edges of the vanes received within the rotor as they traverse the intake portions of the pumping lobes urging the vanes into contact with the cam ring surface.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates generally to rotary vane pumps for motor vehicle power steering systems and more particularly to a cartridge type rotary vane pump exhibiting enhanced cold start performance.

[0003] 2. Description of Related Art

[0004] Motor vehicle power steering systems typically rely upon rotary vane pumps to provide pressurized fluid utilized therein. Such pumps typically are driven by the vehicle engine and are thus oriented for rotation on a horizontal axis. When operating under typical service conditions, rotation creates centrifugal force which drives the vanes outwardly into intimate contact with the lobed, interior surface of the pumping chamber, thereby providing a fluid tight seal and good pumping efficiency.

[0005] During cold starts of the vehicle, especially those at 0° F.(−18° C.) and below, two factors conspire to reduce the output and efficiency of such pumps. First of all, due to their horizontal orientation, upon cessation of rotation, the sole force operating on the vanes is gravity and all those vanes disposed above the horizontal center plane of the rotor retract into the rotor, to the bottom of the rotor vane slots, causing a loss of contact with the pumping chamber surface. Without contact and seal at the tips of the vanes, pump output is reduced. Furthermore, because the viscosity of power steering fluid increases significantly at lower temperatures, centrifugal forces generated by rotation of the rotor and vanes may be insufficient to overcome the viscous frictional drag between the vanes and rotor slots caused by the cold power steering fluid. Once again, pumping efficiency may be reduced.

[0006] Such cold starting issues have been recognized and addressed. For example, U.S. Pat. No. 5,147,183 teaches a rotary vane pump having enhanced cold start priming. Appropriate porting disposed in the pressure plate abutting the rotor and cam ring directs power steering fluid from vane slots pumped by the action of retracting vanes in the direction of rotation across the rotor, through a hole at the base of the extending vane slots, to the outlet ports. Pressure developed at the base of retracting vanes forces extending vanes radially outwardly into contact with the chamber surface.

[0007] A recent improvement in power steering systems is electro-hydraulic power steering systems (EHPAS). In these systems, a variable speed electric motor directly drives a cartridge vane pump. A cartridge vane pump includes a top section, a cam ring having an interior lobed chamber which receives the rotor and vanes as well as axial passageways and a bottom section. The top section and bottom section engage opposite faces of the cam ring and these three components are secured together Such a device is disclosed in U.S. Pat. No. 6,149,409.

[0008] Cartridge vane pumps are also susceptible to cold start inefficiencies as described above and the present invention addresses such inefficiencies.

SUMMARY OF THE INVENTION

[0009] A cartridge vane pump for a motor vehicle power steering system exhibits improved cold start performance. The pump includes a plurality of radially disposed vanes which are received within a rotor which is rotatably supported within a cam ring defining a pumping chamber having two diametrically opposed pumping lobes. An inlet (upper) section and an outlet (lower) section engage the end faces of the cam ring and define suitable passageways which provide fluid into and remove fluid from the pumping lobes. Under vane porting in the inlet section provides high pressure fluid to the inner edges of the vanes received within the rotor as they rotate through angular regions corresponding to the intake portions of the pumping lobes, urging the vanes into contact with the cam ring surface.

[0010] Thus it is an object of the present invention to provide a cartridge type rotary vane power steering pump having enhanced cold start performance.

[0011] It is a further object of the present invention to provide a cartridge type rotary vane pump for use with electro-hydraulic power steering systems having improved cold start performance.

[0012] It is a still further object of the present invention to provide a cartridge type rotary vane pump having passageways and arcuate slots adjacent an end of the rotor which provide high pressure fluid to the inner edges of the rotor vanes during the intake portion of rotor rotation to drive the vanes into contact with the inner surface of the cam ring

[0013] It is a still further object of the present invention to provide a cartridge type rotary vane pump having under vane porting which is provided with high pressure fluid from the pump outlet.

[0014] Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like reference numbers refer to the same component, element or feature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic view of a cartridge type rotary vane pump according to the present invention;

[0016]FIG. 2 is an exploded perspective view of a cartridge type rotary vane pump according to the present invention;

[0017]FIG. 3 is a perspective view of the underside of the top section of a cartridge type rotary vane pump according to the present invention; and

[0018]FIG. 4 is a full, sectional view of a cartridge type rotary vane pump according to the present invention taken along line 4-4 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] Referring now to FIGS. 1 and 2, a cartridge type rotary vane pump having improved cold start performance is illustrated and generally designated by the reference number 10. The rotary vane pump 10 includes a first or upper end section 12, a second or lower end section 14 and a middle or cam ring section 16. The three sections 12, 14 and 16 are coupled together through the agency of a pair of parallel spaced apart stanchions 20 which are secured to the second end section 14. The stanchions 20 preferably include end threaded adjacent axial passageways 22. The stanchions 20 extend through aligned spaced apart parallel apertures 24 in the cam ring section 16 and likewise extend through spaced apart parallel apertures 26 in the first end section 12. A pair of threaded fasteners 28 such as machine bolts or screws may be secured in the threaded passageways 22 to retain the sections 12, 14 and 16 of the pump 10 together as illustrated in FIG. 1.

[0020] The first end section 12 includes a centered, circular axial passageway 32 which aligns with a centered, circular axial passageway 34 in the second end section 14. The axial passageways 32 and 34 receive and support for free rotation therein a shaft 36. The shaft 36 include a central region of male splines 38 which engage and drive female splines 42 on a rotor 44. The rotor 44 defines a plurality, preferably ten, radially disposed slots 46 defining an enlarged generally circular region 48 at their inner termini. Each of the radial slots 46 receives a radially slideable vane 50. The rotor 44 with the vanes 50 is received upon the splines 38 of the shaft 36 within a generally oval pumping chamber 60 defined by an inner cam surface 62 within the cam ring 16.

[0021] In addition to the axial parallel apertures 24, the cam ring 16 defines a first pair of diametrically opposed high pressure outlet passageways 64. Additionally, the cam ring 16 defines a pair of diametrically opposed low pressure inlet passageways 66.

[0022] The second or lower end section 14 also defines a pair of diametrically opposed fluid outlet chambers 74 which collect and deliver high pressure power steering fluid to fluid passageways (not illustrated) exterior to the pump 10. A pair of blind, i.e., closed, fluid pockets 76 may also reside in the second or lower end section 14.

[0023] The high pressure fluid chambers 74 communicate with the high pressure fluid passageways 64 in the cam ring 16. Similarly, the pockets 76 communicate with the low pressure inlet passageways 66 in the cam ring 16.

[0024] Turning now to FIGS. 1 and 3, the first or upper end section 12 includes a pair of blind, i.e., closed, pockets 84 which align with the high pressure passageways 64 in the cam ring 16. A pair of symmetrically disposed and identically configured channels 86 lead from the high pressure pockets 84 to a pair of diametrically opposed arcuate under vane ports 88. The under vane ports 88 radially align with, i.e., reside at an equal distance from the axis of rotation of the rotor 44, the generally circular regions 48 at the inner termini of the slots 46 in the rotor 44 illustrated in FIG. 2. The under vane ports 88 are aligned angularly, i.e., at positions around the axis of rotation of the rotor 44, with the intake regions of the cam ring 16, that is, those regions of increasing diameter. The end section 12 also defines a pair of diametrically opposed inlet ports 92 which communicate both with the low pressure passageways 66 in the cam ring 16 and the appropriate regions of the pumping chamber 60, i.e., those regions having increasing diameter, to provide fluid to the inlet sides of the rotor 44.

[0025] At start up, under cold conditions, at least one half of the vanes 50 will be retracted into the rotor 44 by gravity. The remaining vanes 50 will be driven into the rotor 44 as it rotates through the pumping (exhaust) portion of rotation, i.e., reducing diameter of the inner cam surface 62. Under such cold start conditions, the drag created by the viscous hydraulic or power steering fluid on the vanes 50 tends to inhibit extension of the vanes 50 by centrifugal force. However, the rotor 44 does pump some fluid and the pressure of this fluid is transmitted through the high pressure fluid chambers 74, through the high pressure fluid passageways 64, through the pockets 84 in the end section 12, through the channels 86, through the under vane ports 88 and into the generally circular regions 48 at the inner edges of the vanes 50. The pressurized fluid drives the vanes 50 radially outwardly during the intake portions of rotation of the rotor 44. As fluid pressure increases additional pressure is applied to the inner edges of the vanes 50 and the output flow, pressure and efficiency of the pump 10 rises quickly.

[0026] The foregoing disclosure is the best mode devised by the inventors for practicing this invention. It is apparent, however, that apparatus incorporating modifications and variations will be obvious to one skilled in the art of hydraulic vane pumps. Inasmuch as the foregoing disclosure presents the best mode contemplated by the inventors for carrying out the invention and is intended to enable any person skilled in the pertinent art to practice this invention, it should not be construed to be limited thereby but should be construed to include such aforementioned obvious variations and be limited only by the spirit and scope of the following claims. 

We claim:
 1. A cartridge vane pump comprising, in combination, a housing including a first end section, a second end section and a middle cam ring section disposed between said end sections and defining a pump chamber, said pump chamber defining intake regions of increasing diameter, a rotor defining a plurality of axially and radially extending slots having inner ends and vanes disposed in respective said slots, a shaft extending into said chamber for driving said rotor, and one of said end sections defining arcuate passageways communicating with said inner ends of said vane slots and aligned with said intake regions of said pump chamber in fluid communication with a high pressure outlet of said pump.
 2. The cartridge vane pump of claim 1 wherein said rotor includes a splined opening and said shaft includes splines disposed in said splined opening.
 3. The cartridge vane pump of claim 1 further including a pair of alignment pins extending from said first end section, through said cam ring section and into said second end section.
 4. The cartridge vane pump of claim 1 wherein said pump chamber of said cam ring section defines two lobes and said rotor defines ten slots.
 5. The cartridge vane pump of claim 1 wherein said first end section defines inlet passageways and said second end section defines outlet passageways.
 6. The cartridge vane pump of claim 1 wherein said shaft is received within passageways defined by both end sections.
 7. The cartridge vane pump of claim 1 wherein both of said end sections define arcuate passageways aligned with said intake regions of said pump chamber and communicate with said inner ends of said vane slots.
 8. A cartridge vane pump comprising, in combination, a housing including a first end section, a second end section and a middle cam ring section disposed between said end sections and defining a pump chamber, said pump chamber defining intake regions of increasing diameter, a rotor defining a plurality of axially and radially extending slots having inner ends and vanes disposed in respective said slots, a shaft extending through one of said end sections and into said chamber for driving said rotor, and one of said end sections defining arcuate passageways communicating with said inner ends of said vane slots and angularly aligned with said intake regions of said pump chamber in fluid communication with high pressure outlets of said pump whereby fluid under pressure is provided to inner edges of said vanes.
 9. The cartridge vane pump of claim 8 wherein said rotor includes a splined opening and said shaft includes splines disposed in said splined opening.
 10. The cartridge vane pump of claim 8 further including a pair of alignment pins extending from said first end section, through said cam ring section and into said second end section
 11. The cartridge vane pump of claim 8 wherein said pump chamber of said cam ring section defines two lobes and said rotor defines ten slots.
 12. The cartridge vane pump of claim 8 wherein said first end section defines inlet passageways and said second end section defines outlet passageways.
 13. The cartridge vane pump of claim 8 wherein both of said end sections define arcuate passageways aligned with said intake regions of said pump chamber and communicate with said inner ends of said vane slots. 